1. Field of the Invention
The present invention relates to a development system used for an image formation device, such as a printer, a facsimile, or a copier. More specifically, the present invention relates to a developer circulation system which may be used for circulating a developer to be used in a development system. Especially, the present invention relates to an agitation device which agitates a developer contained in a storage tank of a developer circulation system.
2. Description of Related Art
In general, a developer used in a development system contains a toner which is dispersed in a carrier liquid. Also, a development system includes a development device for carrying out a development process, and a storage tank for storing a developer. In the development system, the developer is transferred to the development device from the storage tank, and the developer which was transferred to the development device is returned to the storage tank so that the developer may be circulated between the two.
However, the concentration of toner in the developer, which is returned to the storage tank from the development device, is not only lowered, but also the size of the toner particles and the dispersibility thereof in the carrier liquid are changed because of the high electric field applied to the developer in the development device. Since a constant image concentration cannot be obtained if the state of the developer is varied, the concentration of the developer is generally controlled to be within a predetermined range during a printing process by using a device which adjusts the state of the developer. In general, the device is placed within the storage tank, and has a rotating agitation member of a propeller shape to agitate a developer by using the agitation member.
However, in the above-mentioned conventional device or technique, since a certain amount of the developer remains in the development device when the developer is circulated during a development process, the amount of the developer in the storage tank is decreased and a sufficient agitation thereof cannot be achieved.
Also, if the agitation process is carried out for a small amount of the developer by using the same conditions for a large amount of the developer, the liquid surface of the developer may be disturbed and air bubbles may be induced in the developer. Moreover, if the surface of the developer is disturbed, the amount of the developer may not be detected in a stable manner. On the other hand, if the agitation condition is changed to be appropriate for a case where the amount of the developer in the storage tank is small, a sufficient agitation process cannot be achieved for the large amount of the developer.
The present invention takes into consideration the above-mentioned circumstances, with an object of providing a developer circulation system having an agitation device which is capable of carrying out an appropriate agitation process regardless of whether it is performed during a development process, i.e., regardless of the amount of the developer in the storage tank.
The present invention provides a developer circulation system including: a storage tank which stores a developer including a carrier liquid and a toner; a development device which carries out a development process using the developer supplied from the storage tank; a developer supply passage through which the developer is supplied to the development device from the storage tank; a developer return passage through which the developer is returned to the storage tank from the development device; a circulation pump which supplies the developer in the storage tank to the development device via the developer supply passage, the circulation pump also returns the developer in the development device to the storage tank via the developer return passage; and an agitation member which agitates the developer in the storage tank, wherein an outlet of the developer return passage and an opening of the developer supply passage are located in the storage tank, so as to promote a flow of the developer generated by the rotation of the agitation member, at positions furthest from each other along a flow of the developer from the outlet of the developer return passage and the opening of the developer supply passage.
In accordance with another aspect of the invention, the above developer circulation system further includes: a level sensor which measures the amount of the developer in the storage tank; an agitation motor which rotates the agitation member; and a control unit which adjusts the rotation speed of the agitation motor to one of the different levels of the rotation speed in accordance with the amount of the developer in the storage tank which is measured by the level sensor.